Railway rails are not fastened rigidly to their sleepers, but are fastened in such a way as to retain a certain flexibility in order to better withstand the numerous stresses to which they are subjected, in particular those resulting from expansions and those imposed by the passage of trains. For this purpose, the longitudinal edges of the foot of each rail are fastened to the sleepers by flexible collars the edges of which bear on the foot of the rails under the action of the clamping bolts screwed into the sleepers or into base plates secured to the sleepers.
In view of the fact that these flexible fastenings are located on both sides of the rail, they permit not only a certain vertical elasticity, but also a transverse elasticity in the sense of a compensation for the overturning movements produced in particular when the railway trains change direction.
Unfortunately, until now it has been necessary to interrupt this elastic fastening of the rails in the region of the points, or at least the points which necessitate the removal, over a certain length, of the foot of the rail on the side of the point in order to permit the lateral displacement of the latter relative to the fixed rails. In fact, the absence of the foot of the rail rules out any possibility of fastening the latter on the side of the movable point. Now, it is precisely in the region of the points, where there is necessarily always a change of direction, that this inner fastening would appear to be important, since it is essential to support the rail against the horizontal overturning moment to which it is subjected in the direction opposite the point.
In order to contain these transverse forces on the rail, they are fastened, on the outer side, i.e. the side opposite that where the foot is removed for the installation of the point, by means of a fastening shoe which is bolted to the web of the rail and which opposes the overturning moment of the latter. However, this rigid fastening with the aid of such a show negates the effect of a conventional elastic vertical fastening which, in theory, would always be possible on this outer side, but which is thus rendered superfluous by the rigid fastening of the shoe.
Now, not only does this rigid fastening disrupt the continuity of the flexibility of the track in the region of the points, but, in addition, it leads to other disadvantages such as, for example, acceleration of wear, maintenance difficulties and the risk of the bolts loosening under the action of the vibrations, etc.